JPH08320302A - Gas detection element and its manufacture - Google Patents

Abstract

PURPOSE: To obtain a gas detection element whose sensitivity with regard to various organic compounds and to a silane-based gas is high and whose mechanical strength and durability are excellent. CONSTITUTION: A sensitive film 4 which is composed of a sintered body sintered by adding 1 to 10wt.% of colloidal silica to a stannic oxide powder having an average particle size of 0.1 to 1μm is layed, in a thickness of 5 to 20μm, on a flat boardlike substrate 2. A heater which can heat the substrate 2 to 200 to 350 deg.C is installed at the substrate, and a gas detection element is formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas detecting element which is durable and has a simple manufacturing process, and a manufacturing method thereof.

[0002]

2. Description of the Related Art Monosilane (SiH ₄ ), dichlorosilane (SiH ₄ ) which spontaneously ignites and burns even at a concentration of several% when contacted or mixed with other gases such as air in semiconductor factories, chemical factories and laboratories. ₂ Cl ₂ ), trichlorosilane (SiHCl ₃ ), phosphine (PH ₃ ), diborane (B ₂ H ₆ ), arsine (AsH ₃ ), etc. are used in large quantities, and these special gases are being used. Accidents that spontaneously ignite and become a fire by leaking into the air are increasing. Therefore, a gas detecting element capable of detecting such a special gas at a low concentration is desired. Also, in general chemical plants and coating factories, leakage of alcohols and solvents is not preferable in terms of process control and working environment, so early detection of these is desired.

Conventionally, Japanese Patent Publication No. 4-68587 and Japanese Examined Patent Publication 6-12 have been used as elements for detecting these minute amounts of gas.
No. 51 publication and the like are known. These are sintered bodies mainly composed of stannic oxide, which is an element that detects a specific gas, such as silane gas, and antimony, platinum, etc. are mixed in these elements, and these are electric resistance values due to adsorption of molecules from the air. Changes. Then, by setting conditions such as the additive to the sintered body of the element and the temperature at the time of detection, it becomes possible to selectively detect a specific gas. However, these conventional devices are disclosed in, for example, Japanese Utility Model Publication No. 2-40532 and "Electrochemical and Industrial Physical Chemistry" Vol. 54, (198).
6 years) No. 9, page 777. As shown in FIG. 4, the main part is made into a paste for sintering powder, and a predetermined amount is taken out, and a cylindrical base having a heater inside. It was necessary to perform a complicated work of applying it to the surroundings of. In addition, unevenness in thickness was caused during coating, which was not efficient and was not satisfactory in strength. Further, it has been desired to further improve the sensitivity of these gas detection elements.

In view of such a point, the present inventor applied a paste containing stannic oxide as a main material to which colloidal silica was added in the form of a thick film on a flat substrate or printing it. The inventors have found that by sintering this, a gas detection element having high mechanical strength, excellent durability, and a simple manufacturing process can be obtained, and the present invention has been accomplished.

[0005]

That is, the present invention is based on the first aspect.
In the gas detection element, a sensitive film is provided on a flat substrate, wherein the sensitive film is 1 to 10% by weight of colloidal stannic oxide powder having an average particle size of 0.1 to 1 μm. It is a sintered body obtained by adding and sintering silica, and is laid on a flat substrate in a thickness of 5 to 50 μm.
The present invention provides a gas detection element characterized in that a heater capable of heating to 350 ° C. is provided. Further, the sensitive film further contains platinum (Pt) and / or palladium (Pd) and has a composition ratio of Pt / Sn to tin (Sn).
There is provided any one or a combination of Sn = 1 to 10 mol% and Pd / Sn = 1 to 10 mol%, and the above gas detection element is provided.

A second aspect of the present invention is the first step of pulverizing stannic oxide powder to an average particle size of 0.1 to 1 μm and drying, and the powder obtained in the first step containing colloidal silica. Second step of adding and mixing 10 to 10% by weight, water or an organic solvent to the powder obtained in the second step, and a third step of forming a paste by adding a binder if necessary, the paste on a flat substrate Provided is a method for producing a sensitive film, which comprises a fourth step of applying 5 to 50 μm (thickness when dried) and drying, and a fifth step of baking the element obtained in the fourth step at 600 to 750 ° C. It is a thing. Furthermore, in any of the steps from the first step to the third step, the platinum compound and / or the palladium compound is mixed with tin (S
The composition ratio to n) is Pt / Sn = 1 to 10 mol%, Pd
/ Sn = 1 to 10 mol% is added to provide the above-mentioned method for producing a sensitive film.

The present invention will be described in more detail below. The gas detecting element of the present invention is shown in FIG. 1, FIG. 2 and FIG.
An example cross-section, top view and rear view are illustrated. In each figure, 1 is a gas detection element, 2 is a substrate, 3 is a heater, 4 is a sensitive film, 5 is an electrode, and 6 is a protective film. The substrate 2 is a hard plate made of porcelain, for example, alumina. The substrate 5, the electrodes 5, the heater 3, and the sensitive film 4 are laminated on the upper and lower surfaces of the substrate, and then divided into chips. The heater 3 is a heating wire made of, for example, platinum or ruthenium oxide, and is mounted on the back surface of the substrate 2 by printing in advance. The sensitive film 4 has an average particle size of 0.1 to 1
It is a sintered body obtained by adding 1 to 10% by weight of colloidal silica to stannic oxide powder of μm and sinter, and is laid on a flat plate substrate to a thickness of 5 to 50 μm. In order to manufacture this sensitive film, it is preferable to manufacture it by the following steps, for example.

First, in the first step, stannic oxide raw material powder is calcined at a temperature of 150 to 700 ° C. for about 2 to 10 hours,
Adjust the surface area and crystallite size of the powder. Then, this is subjected to a ball mill, pulverized to an average particle size of 0.1 to 1 μm, and dried. Next, in the second step, 1 to 10% by weight, preferably 2.5 to 5.0% by weight, of colloidal silica is added to and mixed with this. Next, in the third step, water or an organic solvent is mixed to form a paste. The amount of water or organic solvent blended is not particularly limited, but the viscosity must be such that it can be deposited on the substrate by printing or coating in a uniform thickness. Usually, the amount of water or organic solvent required for this is 20% by weight or less, preferably 10% by weight or less, based on the powder component. In this case, PVA, PEG, vinyl acetate or the like is suitable as the binder. Next, as a fourth step, this paste is printed or applied by a method such as screen printing on a substrate and then dried. The thickness of the film is 5 to 50 μm when dried, preferably 10 to 50 μm.
It is 30 μm.

The substrate used in this fourth step is shown in FIGS.
1 is used as a substrate in which a plurality of substrates 2 shown in FIG. 2 are arranged vertically and horizontally, and at this time, the electrodes 5 on the upper and lower surfaces, the heater 3 and the protective film 6 on the back surface are laminated. Then, after this step, the single substrate is divided at positions such as grooves that are created in advance, and the configuration shown in the figure is obtained. The screen printing method is
Since the mask plate is overlaid on the above-mentioned one substrate and the paste is applied, it is possible to make the number of substrates 2 divided into one substrate at a time. Then, as a fifth step, this is baked at 500 to 750 ° C. to form a sensitive film.

The substrate on which the sensitive film obtained as described above is mounted is preliminarily attached with the heater 3 from the back side, and is further covered with the vitreous protective film 6. The gas detector is completed by attaching it to each electrode 5 and attaching it to the sensor holder. As described above, the substrate used in the fourth step is as shown in FIGS.
1 is used as a substrate in which a plurality of substrates 2 shown in FIG. 2 are arranged vertically and horizontally. At this point, the electrodes 5 on the upper and lower surfaces and the heater 3 on the back surface are used.
And the protective film 6 is laminated. Then, after this step, one substrate is divided at positions such as grooves that are created in advance,
The configuration is as shown. The effect of using this one substrate is common to the whole constitution of each part shown in the figure, and a plurality of electrodes 5 are simultaneously formed on one substrate which is divided into the substrate 2 by vapor deposition of an electrode material such as gold. By applying a paste using a mask material of a heater material such as platinum,
Since the heater 3 is formed, the protective film 6 is formed on the heater 3 by applying a mask plate of a coating material such as molten glass, and the sensitive film 4 is formed on the opposite surface of the heater 3 by the screen printing method. At the same time, it is possible to make a homogeneous and small element.

In the present invention, other components can be added to the sintering raw material mainly containing stannic oxide and containing colloidal silica to improve the selectivity and sensitivity to a specific gas. These components include platinum and palladium compounds. The ratio of these components to tin is Pt / Sn = 1 to 10, preferably 1
-5 mol%, Pd / Sn = 1-10, preferably 1-5
Mol%.

[0012]

In the gas detecting element of the present invention, as described above, the sensitized film mainly composed of stannic oxide and mixed with colloidal silica and sintered is used, and therefore the sensitivity to a trace amount of gas is extremely high. In addition, since we decided to provide a thick sensitive film on a flat base, it is possible to lay a sensitive film with an accurate thickness and pattern without sagging or uneven thickness by printing, and also in the manufacturing process. In terms of quality control, it is possible to obtain a device that is simple and stable, small in size, and excellent in strength.

The present invention will be further described below with reference to examples.

【Example】

Example 1 (Influence of Particle Size) Uncalcined raw material powder (SnO ₂ ) was crushed by a ball mill at different times, and 5% by weight (using 20% aqueous solution) of colloidal silica was added to these powders. Water was added as a solvent to the powder in an amount of 10% by weight, and PEG as a binder was added in an amount of 15% by weight to prepare a paste.
Base made of alumina (1 chip is 2mm x 3mm x
0.5mm), then fire at 650 ℃,
When a sensitive film having a thickness of 10 μm was formed and the sensitivity of the gas detection element using the same to each organic compound (methanol, ethanol, isopropyl alcohol (IPA), toluene) gas was measured, the results shown in FIG. 5 were obtained. Obtained.
In the figure, R ₀ is the electrical resistance of the device in air at 25 ° C., and R _g is 10 of the measured gas of each organic compound.
It is the electric resistance of the element in 0 ppm. In each of the following examples, the same conditions were used unless otherwise specified. As can be seen from the results of FIG. 5, the ball mill treatment time was 1 day (average particle size 0.91 μm) and 3 days (0.79 μm).
μm) and 7 days (0.75 μm), the sensitivity is improved to a certain extent as the particle size becomes smaller, but 0.7
It can be seen that the highest sensitivity is exhibited at 9 μm. It is considered that this is because the pore structure of the sintered body is related to the sensitivity. Generally, the average particle size range desired in the present invention is 0.1 to 1 μm.

Example 2 (Effect of colloidal silica) The content of colloidal silica in stannic oxide, which is a raw material for firing, is in the range of 1 to 10% by weight, preferably 2 to 6% by weight. desirable. Uncalcined, ball-milled stannic oxide powder (average particle size 0.75 μm) for 1 week and colloidal silica 2.5, 5.0, 10.0, 2 respectively.
When added in an amount of 0.0% by weight, the thick film was printed in the same manner as in Example 1 and baked at 650 ° C., and the sensitivity was measured. The results shown in FIG. 6 were obtained. As can be seen from FIG. 6, when it exceeds 10% by weight, it gradually decreases. It is considered that this is because when the silica content becomes high, excess silica penetrates into the contact portion of the particles and acts to separate the particles. The effect of adding this colloidal silica is 750 ° C.
It is to obtain a sintered body with sufficient strength even by firing below.

Example 3 (Effect of firing temperature) In order to see the effect of the firing temperature of the raw material powder on the sensitivity of the element, stannic oxide powder (average particle size 0.75 μm, uncalcined and ball-milled for 1 week) was used. ) Was added with 5.0% by weight of colloidal silica, which was thick-film printed in the same manner as in Example 1 and then fired at several temperatures in the range of 500 to 750 ° C. to measure the sensitivity. However, the result as shown in FIG. 7 was obtained. As can be seen from FIG. 7, the highest sensitivity was obtained at 650 ° C., and the desired sensitivity was not obtained at a temperature lower than 600 ° C. and a temperature higher than 750 ° C. Of course, the optimum firing temperature changes when a compound such as antimony or platinum is added. In the case of platinum, it does not change much, but in the case of doping with antimony, the firing temperature is 700-
It is as high as 800 ℃.

Example 4 (Effect of Thickness of Sensitive Film) Sensitivity was measured by changing the film thickness by repeating the printing times of the paste, and the results shown in FIG. 8 were obtained. As you can see,
It can be seen that the thinner the film thickness, the higher the sensitivity, but when it exceeds 50 μm, the sensitivity decreases. However, if the film thickness is thinner than 5 μm, a uniform film having sufficient strength cannot be obtained, which is not preferable.

Example 5 (Effect of Heater Temperature) 5.0 wt% of colloidal silica was added to stannic oxide powder which had not been calcined and was ball-milled for 1 week. After printing the film, the device was prepared by firing at 650 ° C., and the sensitivity was measured by changing the heater temperature variously, and the results shown in FIG. 9 were obtained. As can be seen from FIG. 9, the maximum sensitivity was given at around 300 ° C.

Example 6 (Sensitivity of Thick-Film Sintered Body to Silane Gas) 5.0 wt% of colloidal silica was added to stannic oxide powder which had not been calcined and was ball-milled for 1 week. After printing a thick film in the same manner as above, the device was prepared by firing at 650 ° C., and the sensitivity of the device to various silane gas concentrations was measured at a heater temperature of 330 ° C. The results are shown in Table 1.

[0019]

[Table 1]

As can be seen from Table 1, R ₀ / R _g also rises corresponding to the rise in the concentration of the silane gas. It can be seen that the silane gas alarm has sufficient sensitivity even with an alarm concentration of 5 ppm required.

Example 7 To a raw material powder obtained by ball-milling an uncalcined raw material powder (SnO ₂ ) for 1 week, 5.0% by weight of colloidal silica was added, and palladium chloride as a catalyst was added to Pd / S.
After n = 1 mol% was added, a thick film was printed in the same manner as in Example 1 and then baked at 650 ° C. to prepare a device, and the sensitivity was measured. As shown in Table 2, this sensor showed higher sensitivity to toluene and hexane (100 ppm in both cases), which are usually low in sensitivity, than the sensor without palladium added.

[0022]

[Table 2]

When the amount of palladium added is increased as described above, the sensitivity becomes low at Pd / Sn = 10 mol%. Therefore, the addition of palladium exceeding Pd / Sn = 10 mol% has no further effect. Similarly, a device was similarly prepared using a chloroplatinic acid aqueous solution instead of palladium chloride, and the sensitivity was measured.
Similar results were obtained. That is, Pt /
Sn = 1 to 10 mol% is effective. Furthermore, if palladium or platinum is added as a catalyst, the resistance value of the element becomes several times higher. Therefore, by using antimony oxychloride and simultaneously adding an appropriate amount of Sb / Sn = 2 to 8 mol%, the resistance value can be increased. Can be prevented from increasing.

[0024]

As described above, according to the present invention, 1 to 10% by weight of colloidal silica is added to stannic oxide powder having an average particle size of 0.1 to 1 μm on a flat substrate. The sensitive film of the sintered body added and sintered has a thickness of 5 to 20 μm.
Since the substrate is a gas detection element provided with a heater capable of heating the substrate to 200 to 350 ° C., it has high sensitivity to various organic compounds and silane-based gases, and has high mechanical strength and durability. An excellent gas detection element can be obtained.

[Brief description of drawings]

FIG. 1 is a sectional view of an example of a gas detection element of the present invention.

FIG. 2 is a plan view of an example of a gas detection element of the present invention.

FIG. 3 is a rear view of an example of the gas detection element of the present invention.

FIG. 4 is a diagram showing an example of a conventional gas detection element.

FIG. 5 is a diagram showing a change in sensitivity depending on the average particle size of particles.

FIG. 6 is a diagram showing a change in sensitivity depending on the content of silica.

FIG. 7 is a diagram showing a change in sensitivity depending on a firing temperature.

FIG. 8 is a diagram showing a change in sensitivity with film thickness.

FIG. 9 is a diagram showing a change in sensitivity depending on a heater temperature.

[Explanation of symbols]

 1 gas detection element 2 substrate 3 heater 4 sensitive film 5 electrode 6 protective film

Claims (6)

[Claims] 1. A gas detection element comprising a flat substrate and a sensitive film provided on the flat substrate, wherein the sensitive film has an average particle size of 0.1.
A sinter obtained by adding 1 to 10% by weight of colloidal silica to stannic oxide powder of ˜1 μm and sintering the sinter, which is laid on a flat substrate to a thickness of 5 to 50 μm. A gas detecting element, characterized in that a heater capable of heating this to 200 to 350 ° C. is provided. 2. The sensitive film further comprises platinum (Pt) and / or
Alternatively, the composition ratio of palladium (Pd) to tin (Sn) is Pt / Sn = 1 to 10 mol%, Pd / Sn = 1 to 1
The gas detection element according to claim 1, wherein any one or a combination of 0 mol% is contained. 3. The sensitive film is characterized in that silicon oxide is discontinuously carried on the surface of the device.
The gas detection element according to 1. 4. Stannous oxide powder having an average particle size of 0.1 to 1
First step of pulverizing to dryness to μm and drying, second step of adding 1 to 10% by weight of colloidal silica to the powder obtained in the first step and mixing, water or organic to the powder obtained in the second step Obtained in the third step of adding a solvent and, if necessary, a binder to form a paste, the fourth step of applying the paste to a flat substrate to a dry film thickness of 5 to 50 μm and drying, and the fourth step. A sensitive film is manufactured by a fifth step of baking the device at 600 to 750 ° C.
To a method for manufacturing a gas detection element, which comprises attaching a heater to the substrate during the fifth step. 5. A platinum compound and / or a palladium compound having a composition ratio of Pt / Sn = 1 to 1 to tin (Sn) in any one of the first to third steps.
The method for producing a gas detection element according to claim 4, wherein the addition is performed at 10 mol% and Pd / Sn = 1 to 10 mol%. 6. The method for producing a gas detection element according to claim 4, wherein the platinum compound is added as a chloroplatinic acid aqueous solution.